It has been proposed in U.S. Pat. No. 3,841,953 to form nonwoven webs of melt blown fibers using polymer blends, in order to obtain webs having novel properties. A problem with these webs however is that the polymer interfaces causes weaknesses in the individual fibers that causes severe fiber breakage and weak points. The web tensile properties reported in this patent are generally inferior to those of webs made of corresponding single polymer fibers. This web weakness is likely due to weak points in the web from incompatible polymer blends and the extremely short fibers in the web.
A method for producing bicomponent fibers in a melt-blown process is disclosed in U.S. Pat. No. 4,729,371. The polymeric materials are fed from two conduits which meet at a 180 degree angle. The polymer flowstreams then converge and exit via a third conduit at a 90 degree angle to the two feed conduits. The two feedstreams form a layered flowstream in this third conduit, which bilayered flowstream is fed to a row of side-by-side orifices in a melt-blowing die. The bi-layered polymer melt streams extruded from the orifices are then formed into microfibers by a high air velocity attenuation or a "melt-blown" process. The product formed is used specifically to form a web useful for molding into a filter material. There is not disclosed a stretchable, high loft, and preferably high strength web.
U.S. Pat. No. 4,753,843 (Cook et al) discloses a multi-layer nonwoven web, generally melt-blown polypropylene, where the outer layers are rendered hydrophilic by spraying on a surfactant. The center layers remain hydrophilic. The web is designed to provide wipes that will absorb both aqueous liquids and oils without streaking. Another multi-layer web is discussed in U.S. Pat. No. 4,436,780 (Hotchkiss). In Hotchkiss, only the center layer is a nonwoven web with outer layers of a continuous filament spun bond web. The use of a surfactant is discussed but apparently not exemplified. The web allegedly displayed improved streak free performance over similar prior art webs (FIG. 4) and both oil and water absorbency attributed primarily to the nonwoven web layer.
A single layer wipe using melt-blown microfibers is described in U.S. Pat. No. 4,426,417 (Meitner et al) where staple and cotton fibers are incorporated into the web. Better clean wiping is attributed to the staple and cotton fibers as is improved strength over comparable webs using added pulp as discussed in U.S. Pat. No. 4,100,324 (Anderson et al). This provides an allegedly low density web compared to pure nonwoven webs.
Although the above webs provide varying desirable combinations of properties, there are still needs to provide webs of improved properties (such as strength, absorbance capacity, etc.) or similar properties by improved or similar processes. For example, it can be difficult to incorporate stable and cotton fibers into a web as discussed by Meitner et al in Pat. No. 4,426,417 while expected variations in raw materials can lead to unwanted variability in web performance.